156 



Dr. W. Kowalevsky on the 



[Feb. 6, 



Early Eocene Paridigitata. 



/On 



Paridigitata with 

 crescentic teeth <J 

 (Selenodonta). 



□ □ 



Tubercular-toothed Crescentic-toothed 

 Paridigitata. Paridigitata. 



lowed a twofold mode of descent, one of which I term the inadaptive, and 

 the other the adaptive, thus, finally, giving rise to four distinct groups : — 



A. The group following the inadaptive reductions 

 develop enormously in Eocene and Middle Miocene 

 times : all have distinct metacarpalia and metatar- 

 salia, five-lobed upper molars, smooth distal extre- 

 mities of the metapodials. Genera : Bothriodon, Di- 

 chobune, JRhagatJierium, Cainotherium. They reached 

 their highest development and culminated in the di- 

 dactyle Anoplotherium, Xiphodon, and Diplopus, 

 which all became extinct without direct successors. 



B. The group following the adaptive reduction 

 separated from the group A somewhere in the 

 Middle Eocene, by some of the small Hyopotamidce 

 acquiring four-lobed upper molars, as met with at 

 Mauremont, and becoming Dichodons. Intermediate 

 stages little known; the Gelacus is one of them. 

 The least reduced living form is Hyomoschus. Cul- 

 minating in recent times in the didactyle Bovidce and 

 Antilopidai. 



A. Group following the inadaptive reduction 

 very little known. Acotherulum and another larger 

 hog-like animal from the Middle and Upper Eocene 

 may belong to this group ; they were certainly tetra- 

 dactyle. Culminated in the lowest Miocene in the 

 didactyle Entelodon : no successors. 



B. Group following the adaptive reduction, 

 branched from the group A in the Eocene ; the most 

 typical representative is the Ghoerotherium from 

 Sansans, with the phalangeal ridge not yet extend- 

 ing over the whole distal end of the metapodium. 

 Palceochoerus : reduction has fairly set in on the 

 adaptive mode, the phalangeal ridge passing over 

 the whole end of metapodial. Sus still more reduced. 

 Dicotyles : all the distal surface of the carpus and 

 tarsus taken by the enlarged middle digits. Tending 

 to become didactyle. 



Paridigitata with 

 tubercular teeth 

 (Bunodonta or 

 Suina). 



< 



